1. Field of the Invention
This invention relates generally to a method and apparatus for computing the life expectancy of equipment and more particularly the life expectancy of electrical power transformers.
The useful life of many devices is greatly influenced by the temperature at which it operates. Additionally, this temperature effect is cummulative. One such device is a transformer. Owners of large transformers have large capital investments which they want to protect from abuse and, shortened life expectancy, but at the same time, want to get the most utilization from that investment by loading the transformer as much as possible. Since heat generated within a transformer caused by winding loss, is a function of the loading on the transformer, the temperature of the windings of the transformer is also a function of transformer loading. The owner must, therfore balance the loading of the transformer against the consumption of its expected life to achieve an optimum use of his investment.
Insulation deterioration and, therefore, life expectancy with respect to temperature and time, follows an adaptation of the Arrhenius function that states that the logarithm of insulation life is a function of the reciprocal of the absolute temperature.
2. Description of the Prior Art
Owners of transformers currently monitor winding temperature using either simulations or direct measurements with indicators which record the highest achieved temperature. Such devices, however, do not account for the time function of the temperature effect on life expectancy and, therefore, provide little information as to the actual life consumption of the transformer windings.